1. Field of the Invention
The present invention generally relates to a battery protecting circuit which protects plural secondary batteries connected in series, and a battery protecting device. Further, the present invention relates to a battery pack having the battery protecting device.
2. Description of the Related Art
An example of a lithium-ion secondary battery is formed by a multistage stack of plural cells. However, when a line or the like between the lithium-ion secondary battery and a monitoring terminal for monitoring the cell voltages of the cells is broken and disconnected, the corresponding cell voltage cannot be accurately monitored. Therefore, if the charged state of the cell is an abnormal state such as overcharge or overdischarge, the abnormal state may not be detected. The battery protecting circuit may have a disconnection detecting function in order to avoid such an abnormal state. Patent Document 1 discloses a method of detecting disconnection by pulling up or down the monitoring terminal using a constant current circuit to shift the electric potential of the monitoring terminal when the disconnection of the monitoring terminal occurs.
[Patent Document 1] Japanese Laid-open Patent Publication No. Hei 8-308115